Tumoral lymphocyte immune response to preoperative radiotherapy in locally advanced rectal cancer as a prognostic factor for survival: the LYMPHOREC study
Présentation PosterInternational audienceBackground: Short-course preoperative radiotherapy (sc-preopRT) and long-course preoperative radiotherapy (lc-preopRT) followed by total mesorectal excision (TME) are worldwide standards of care in locally advanced T3–4 N0 or N1 rectal adenocarcinoma. It is now well established that the host immune system participates in the elimination of tumor cells and that significant tumor infiltration by T-cells (LT), such as CD8+, is associated with a better prognosis. In colorectal tumors, the infiltration of Treg FoxP3+ is also described as a prognostic factor associated with better survival. We aimed to investigate the impact of the immune response to preoperative RT on progression-free survival (PFS) and overall survival (OS) in rectal cancer managed with TME.Material and Methods: We analyzed data for 237 patients with rectal cancer who underwent TME between 1995 and 2007 after neo-adjuvant treatment with preoperative RT with or without CT in 3 French centers. The LYMPHOREC study was approved by the French national review boards and independent ethics committee (CPP, CCTIRS and the CNIL). Our primary objective was to assess the impact of the immune infiltration of the tumor or tumor site (in cases with complete response) by CD8+ and FoxP3+ lymphocytes after sc-preopRT or lc-preopRT with or without CT on progression-free survival (PFS) and overall survival (OS). Our secondary objectives were to assess changes in the quantities of these lymphocyte infiltrations with respect to the type of preoperative RT (with vs without chemotherapy) or the dose fractionation scheme (≤2Gy vs >2Gy/fraction). These second analyses were performed with 133 patients from whom one biopsy sample was collected. A biopsy-based pretherapeutic lymphocyte infiltration was thus evaluated.Results: In univariate analysis, TNM stage, the delay between surgery and RT, CD8+, FoxP3+ and the ratio CD8+/FoxP3+ were significantly correlated with survival outcomes while chemotherapy as a component of preoperative radiotherapy was not. In multivariate analysis, when adjusted for clinical and treatment-related variables, tumor infiltration by FoxP3 lymphocytes after treatment significantly correlated with PFS (p=0.007). Variations in the CD8/FoxP3 ratio inside the epithelial tissue from before to after preoperative RT correlated with PFS and OS (p=0.049 and p=0.024, respectively). Interestingly, the dose per fraction (<2Gy vs. ≥2Gy) significantly influenced the CD8/FoxP3 ratio after treatment (p=0.027) with a lower ratio with hypofractionated RT.Conclusions: Patients with rectal cancer who had a significant decrease in the CD8/FoxP3 ratio after preoperative radiotherapy had better survival outcomes. The CD8/FoxP3 ratio needs to be validated prospectively. The immune response to preoperative RT may guide physicians in the decision to give adjuvant treatment to patients with rectal cancer